The invention relates to a process for the preparation of ethanolamines (I) by conversion of ethanolamines (II) different from these.
Alkanolamines are basis products for a large number of industrial applications.
Ethanolamines, such as triethanolamine (TEA), or secondary products thereof are used, for example, in washing liquids for gas washes, in crop protection compositions, soaps, laundry detergents and shampoos, and as dispersants and emulsifiers.
Ethanolamines can be prepared by hydroxyethylation of amines by reaction of the amines with ethylene oxide, see Ullmann""s Encyclopedia of Industrial Chemistry, chapter on ethanolamines and propanolamines-N-alkylated ethanolamines.
Monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) are prepared by reacting ammonia with ethylene oxide in the liquid phase under pressure and at elevated temperature, as described in GB-A-760 215 or EP-A-673 920.
In this process, an ethanolamine mixture is formed which comprises, as main components, MEA, DEA and TEA, which is then worked up by distillation in a plurality of stages. The composition of the resulting ethanolamine mixture can only be varied within narrow limits as a consequence of the process. In the preparation of an ethanolamine, for example of DEA, the other ethanolamines (MEA, TEA) thus automatically form as coupling products. If, for example, there is a high requirement for DEA, then this can only be satisfied under some circumstances by an overproduction of the coupling products MEA and TEA being accepted.
There has therefore been no lack of attempts to produce a particular ethanolamine by conversion of other ethanolamines.
U.S. Pat. No. 4,264,776 describes the catalytic oxidation of tertiary amines with oxygen to secondary amines in the presence of an active carbon catalyst. According to
Example 2 of this patent specification, TEA is reacted over active carbon at 115xc2x0 C. with 60% conversion to DEA with undefined selectivity. A C2 radical of the TEA is degraded oxidatively in the process, e.g. to formic acid.
U.S. Pat. No. 4,328,370 describes the conversion of lower trialkanolarnines to mono and dialkanolamines by reaction with ammonia at elevated temperature in the presence of a hydrogenation catalyst. According to the examples of this patent specification, TEA can be reacted with ammonia in the presence of Pd/C or Pd/Al2O3 and optionally H2 at 200 to 300xc2x0 C. to give DEA and MEA. The selectivity of the formation of DEA and MEA decreases with increasing conversion. The total yield of MEA and DEA (sum) is up to 50% at a conversion of 66% and a selectivity of 79.7%.
U.S. Pat No. 5,693,866 describes the treatment of alkanolamines with alkali metal hydroxides for the purpose of improving the color quality of the alkanolamines, the alkanolamines being chemically unchanged. In the examples, TEA is treated with NaOH at temperatures of from 165 to 176xc2x0 C. over a period of from 3 to 65 h.
It is an object of the present invention to provide an economic and efficient process for the preparation of one or more ethanolamines (I) from one or more ethanolamines (II) different from the ethanolamines (I) in order to utilize ethanolamines (II) produced in excess in an economically sensible manner.
We have found that this object is achieved by a process for the preparation of one or more ethanolamines (I), chosen from the group consisting of monoethanolamine, diethanolamine and triethanolamine, by conversion of one or more ethanolamines (II) different from the ethanolamine(s) (I), chosen from the group consisting of monoethanolamine, diethanolamine, triethanolamine, O,N,N-tris (2-hydro-xyethyl)ethanolamine, N-(2-amino ethyl) ethanolamine, N-(2-hydroxyethyl)piperazine, N-(2-hydro-xyethyl) morpholine and N,Nxe2x80x2-bis(2-hydroxyethyl) piperazine, where the ethanolami ammonia, is/are treated with a strong base.
The ethanolamine(s) (I) can be prepared from a single ethanolamine (II) or a mixture of two or more ethanolamines (II).
For example, diethanolamine can be obtained by treatment of pure monoethanolamine or of pure triethanolamine with a strong base. Monoethanolamine can be obtained by treatment of pure diethanolamine. In addition, triethanolamine is generally obtained.
Diethamolamine is preferably prepared by treatment of a mixture comprising monoethanolamine and triethanolamine with a strong base. Preferred mixtures comprise TEA and MEA in the molar ratio from 10:1 to 1:10.
The treatment of the ethanolamine(s) (I) can be carried out in the presence of ammonia. For example, diethanolamine can be prepared by treatment of a mixture comprising triethanolamine and ammonia.
In addition, monoethanolamine is generally obtained. Preferred mixtures comprise TEA and ammonia in the molar ratio of from 10:1 to 1:20.
Monoethanolamine can also be obtained by treatment of a mixture comprising diethanolamine and ammonia.
Said ethanolamine mixtures used in the conversion can comprise further ethanolamines. It is also possible to use complex ethanolamine mixtures which comprise two or more or all of the ethanolamines (II) listed above. The starting ethanolamine mixture can in part already comprise the ethanolamine(s) (I) to be prepared. Examples are technical grade ethanolamine mixtures as can be obtained by the following processes:
by reaction of ammonia or of a primary or secondary amine with ethylene oxide. e.g. in accordance with EP-A-673 920:
by 1,4-addition of ammonia or of a primary or secondary amine to an xcex1,xcex2-unsaturated aldehyde, such as acrolein, and subsequent hydrogenation;
by 1,4-addition of ammonia or of a primary or secondary amine to an xcex1,xcex2-unsaturated acid.such as acrylic acid, or to an xcex1,xcex2-unsaturated ester, such as acrylic ester. and subsequent reduction., e.g. by hydrogenation:
by 1,4-addition of water to an xcex1,xcex2-unsaturated nitrile, such as acrylonitrile, and subsequent reduction, e.g. by hydrogenation;
by amination of primary or secondary alcohols or reductive amination of hydroxyaldehydes or hydroxyketones. N-(2-Aminoethyl)ethanolamine (AEEA) can be obtained by reaction of monoethanolamine or ammonia with ethylene oxide in the presence of hydrogen and a hydrogenation, dehydrogenation or amination catalyst.
Preference is given to starting from ethanolamine mixtures which do not comprise the product of value (the ethanolamine (I) to be prepared) since the product of value can also gradually be degraded under the reaction conditions.
It is assumed that, under the action of strong bases, there is a cleavage of ethanolamines with n 2-hydroxy-ethyl groups into the next lower ethanolamine with nxe2x88x921 2-hydroxyethyl groups and ethylene oxide. The ethylene oxide which is formed as an intermediate is scavenged by an acceptor, preferably ammonia or monoethanolamine, to form the corresponding next higher ethanolamine. It is therefore preferred according to the invention to prepare an ethanolamine with n 2-hydroxyethyl groups from a mixture of an ethanolamine with n+1 2-hydroxyethyl groups and an ethanolamine with nxe2x88x921 2-hydroxyethyl groups or ammonia. Ethylene oxide is also released from the other ethanolamines specified (O,N,N-tris (2-hydroxyethyl)ethanolamine, N-(2-amino ethyl) ethanolamine, N-(2-hydroxyethyl)piperazine, N-(2-hydroxyethyl)morpholine and N,Nxe2x80x2-bis(2-hydroxy ethyl) piperazine), which generally do not represent a product of value. These may therefore be likewise advantageously present in the starting mixture. The 2-hydroxyethylamino units (HO-CH2-CH2-N) present in the starting material mixture are largely retained overall.
The process according to the invention makes it possible, in particular, to convert economically significant ethanolamines. such as MEA, DEA and TEA, into one another, in particular to prepare DEA from MEA and/or TEA. By-products produced in this reaction are coupling products, such as N,Nxe2x80x2-bis (2-hydroxyethyl)piperazine. O-ethoxylated products, such as O-(2-hydroxyethyl)triethanolamine, and products with higher degrees of ethoxylation. In contrast to the prior art, however, these products are not discarded, but can be used, for example, as cement auxiliaries.
The ethanolamine(s) (II) is/are treated with a strong base. Suitable bases are all strong bases which are able to deprotonate ethanolamines to a noteworthy degree. Preferred strong bases are basic alkali metal and alkaline earth metal hydroxides, alkali metal alkoxides, and basic metal oxides, such as oxides of the rare earth metals, for example LiOH, NaOH, KOH, CsOH, Ba(OH)2, Ca(OH)2, sodium methoxide, sodium ethoxide, potassium t-butoxide and lanthanum oxide. The bases can be used as solid or as aqueous or alcoholic solution. Particularly preferred strong bases are NaOH and KOH.
The ethanolamine(s) (II) can be present dissolved or dispersed in an inert solvent. Suitable solvents are alcohols, such as methanol, ethanol, isopropanol, n-butanol, 2-ethylhexanol, ethers, such as tetrahydrofuran and 1,4-dioxane, aliphatic and aromatic hydrocarbons or mixtures thereof, such as pentane, hexane, heptane, petroleum ether, benzene, toluene, xylene, Mihagol and water.
The process according to the invention is generally carried out at temperatures above 180xc2x0 C., preferably at 180 to 270xc2x0 C., particularly preferably at 190 to 260xc2x0 C., and in particular at 200 to 250xc2x0 C. in customary reaction apparatuses, such as autoclaves, tubular reactors or stirred-tank reactors. The reaction time is preferably between 0.5 and 20 h and is governed by the composition of the starting mixture, the desired product of value, the strong base used and the reaction temperature. The choice of these parameters can be optimized directly by the person skilled in the art by a few exploratory experiments. Reaction times which are too long may reduce the yield of the product of value since the product of value may also be subjected to cleavage under the reaction conditions. It is particularly preferable to continuously remove the product of value formed, for example by distillation, from the reaction mixture and thus to protect it against degradation.